Only three of some 150 electra dolphins are believed to have been saved, after being washed ashore in the Ibaraki Prefecture. Scientists are trying to explain the incident, while some see it as an ominous sign to a similar case before the 2011 earthquake.

At least 149 melon-headed whales, a species of dolphin, were found at the Hokota beach on Friday, according to local officials. Rescue efforts were abandoned as night fell, and only a handful of mammals could be saved.

“It was becoming dark and too dangerous to continue the rescue work at this beach, where we could not bring heavy equipment,” an unnamed Hokota municipal official told AFP. “Only three of them have been successfully returned to the sea, as far as we can confirm.”

Rescuers, most of whom were volunteers, tried to save the dolphins by pouring water on them, to prevent their skin from getting too dry.

Videos from the scene showed rescuers trying to release the dolphins back into the ocean, but the tide washed the weak animals back onto the beach. Photos revealed that some were badly cut and had deep gashes.

The reason for the mass beaching has not yet been established. Tadasu Yamadao, a researcher at the National Museum of Nature and Science suggested that the dolphins might have got confused and lost.

“Sonar waves the dolphins emit might have been absorbed in the shoals, which could cause them to lose their sense of direction,” Yamadao told the Yomiuri Shimbun newspaper.

However, social media users recalled a similar incident occurred a week before the March 11, 2011 earthquake that resulted in a devastating tsunami that killed tens of thousands of people. About 50 electra dolphins were washed ashore in a similar area on March 3, 2011.